Coaxial band rejection filter with helical line center



March 31, 1970 M. COHEN COAXIAL BAND REJECTION FILTER WITH HELICAL LINE CENTER Filed Oct. 4. 1968 GYROMAGN ETIC SDH EFZE ac gy- 7 DOTATABLE QOD 3 I T bw-1mc db F904 & L. 3

ldb 1.25 db 1 i r T 'F -36oomc United States Patent Oflice Patented Mar. 31, 1970 3,504,305 COAXIAL BAND REJECTION FILTER WITH HELICAL LINE CENTER Morris Cohen, Oceanside, N.Y., assignor to Lora] Corporation, Scarsdale, N.Y.

Continuation-in-part of application Ser. No. 541,415,

Mar. 4, 1966. This application Oct. 4, 1968, Ser.

Int. Cl. H03h 7/10; H01p N32 US. Cl. 333-241 4 Claims ABSTRACT OF THE DISCLOSURE A non-reciprocal coaxial band rejection filter including a hollow outer conductor member, an inner conductor member disposed coaxially within said outer conductor member, said inner conductor member including a non-conductive dielectric rod, a pair of conductive segments interconnected coaxially at the ends of said non-conductive rod, a helical coil of conductive wire interconnecting said conductive segments and wound about said non-conductive rod, and a sphere of gyromagnetic material positioned in the area of said helical coil.

cost, thereby permitting consequent wide sale, distribution and use.

Yet another object of the invention lies in the provision of an improved coaxial non-reciprocal directional preselector employing two helical line structures in coupled relationship.

These objects, as well as other incidential ends and advantages, will more fully appear in the progress of the following disclosure, and be pointed out in the appended claims.

In the drawing, to which reference will be made in the specification, similar reference characters have been employed to designate corresponding parts throughout the several views.

FIGURE 1 is a fragmentary view in perspective showing a first embodiment of the invention.

FIGURE 2 is a schematic view in elevation showing a second embodiment of the invention.

FIGURE 3 is a vertical sectional view as seen from the plane 33 in FIGURE 2.

FIGURE 4 is a graph illustrating typical performance obtained when using the first embodiment.

The disclosed embodiments employ the properties of a sphere of gyromagnetic material disposed in the vicinity of a conductor carrying microwave propagation. A necessary requirement for non-reciprocity is that the microwave magnetic field, usually provided by a magnet, in the region of the sphere be circularly polarized. While this requirement is easily met in such devices as rectangular or cylindrical wave guides, in coaxial lines propagating the TEM mode, the microwave magnetic field is linearly polarized at all points, and therefore any ferrite effects will be completely reciprocal.

I have found that by the use of a helical line center conductor, it is possible to distort the mode pattern to yield a component of the externally applied RF magnetic field in the direction of propagation, so as to permit a high degree of non-reciprocity. Broadly speaking, the disclosed embodiments include a round or square outer conductor and a round center conductor at each end thereof, the center conductors being separated by a dielectric form around which a helix of wire is wound and connected to the ends of the center conductors forming a composite continuous inner conductor. A sphere of gyromagnetic material is inserted through a small hole in the outer conductor and placed near the helical line, to be supported by a rotatable dielectric rod.

Referring now to FIGURE 1 in the drawing, the first embodiment of the invention, generally indicated by reference character 10, comprises: an outer conductor member .11, an inner conductor element 12, a gyromagnetic element 13, and an external DC magnetic field source H such as an external magnet (not shown).

The outer conductor member 11 is illustrated as being of square cross-sectional configuration, but it will be understood that Where desired, a cylindrical outer con ductor member may be employed with equal efiiciency. The member 11 includes an upper wall 15, a lower wall 16 and side walls 17 and 18.

The inner conductor element 12 includes lengths 19 of metallic conductive material interconnected by a dielectric rod 20 of suitable length. A wire conductor 21 interconnects the lengths 19 by being suitably soldered or otherwise interconnected to the outer surfaces thereof and is wound in a number of convolutions 25 about the dielectric rod 20.

The gyromagnetic element 13 includes a sphere 28 of gyromagnetic material and a rotatable supporting rod 29 penetrating an opening (not shown) in the outer conductor member 11. The sphere 28 overlies the dielectric rod 20, and is positioned in the interstice formed between the helical convolutions and the inner surface of the outer conductor 11. As is known in the art, the rod 29 is rotatable about its own axis for adjusting for optimum selectivity, and tuning is accomplished by varying the external DC field.

Referring to FIGURE 4 in the drawing, a device similar to that illustrated in FIGURE 1 was constructed to the following specifications:

Overall length-6 inches Outer conductor ID0.495 inch Inner round conductor0.215 inch Length of dielectric1.5 inches Helix wireNo. 24

Pitch-10 turns/inch Gyromagnetic material-50 mil YIG sphere line withAH=0.6 oe'rsted The external magnetic field was supplied by a Varian magnet.

As seen in FIGURE 4, the insertion loss of the device was approximately 1.0 db when the YIG sphere was not resonated. When the sphere was resonated with the DC field in the direction shown by the solid arrow in FIG URE 1, a 40 db band reject response was noted (indicated by a solid line). When the field was reversed the response was as shown by the dashed line on the graph, approximately 1.25 db. It is evident that the structure is substantially non-reciprocal.

Referring to FIGURES 2 and 3, a second embodiment of the invention, generally indicated by reference character 30, in the form of a non-reciprocal directional preselector, is illustrated.

The device includes an outer housing element 31 supporting a magnet 32 which provides the required external magnetic field. For convenience in manufacturing, the housing element 31 is formed to include first and second parts 33 and 34, respectively, separated by a metallic membrane 34a, housing a lower coaxial conductor 35 connecting first and second ports 36 and 37, respectively; and an upper coaxial conductor 38 connecting third and fourth ports 39 and 40, respectively. The conductors 35 and 38 are substantially similar, each including a rectangular outer conductor member 41 and an inner cylindrical conductor 42.

An opening is cut through the interconnected portions of the parts 33 and 34, and the membrane 34a, and the interconnected portions of the parts 35 and 38 to accommodate a rotatably mounted dielectric rod 43 supporting a gyromagnetic sphere 44, the membrane 340 forming a coupling iris therefor. Each inner conductor member 42 includes a length of dielectric material supporting a helical winding 45, applied as shown in the first embodiment, and with the pitch of each in the same direction. It will be understood that although only a single gyromagnetic sphere is illustrated, it is possible to use a pair of such spheres disposed on either side of a coupling iris (not shown) for superior selectivity, as is known in the art.

During operation of the second embodiment, with the gyromagnetic sphere in non-resonant condition, power entering port 36 does not couple through the sphere, but instead proceeds directly to a matched load or matched detector (not shown) at port 37. When the gyromagnetic sphere is resonated by a magnetic field produced by the magnet 32, power entering the port 36 is coupled through the sphere to port 40 (with the helix wound as above), and any reflections from port 40 do not couple back to port 36 due to non-reciprocity but instead go to port 39. If port 40 is matched, port 39 is decoupled. The operation may be reversed by merely reversing the direction of the direct current magnetic field supplied by the magnet 32.

I wish it to be understood that I do not consider the invention limited to the precise details of structure shown and set forth in this specification, for obvious modifications will occur to those skilled in the art to which the invention pertains.

I claim:

1. A coaxial microwave band rejection filter comprising: a length of coaxial tubing including a hollow outer conductor member, an inner conductor member substantially concentrically disposed with respect to said outer conductor member, said inner conductor member includ ing a pair of conductive segments, 'a dielectric rod positioned coaxially between said conductive segments, said dielectric rod having an outer surface, a conductive wire disposed in helical convolutions upon said outer surface, the ends of which are interconnected to said conductive segments, a sphere of gyromagnetic material supported in the interstice between said inner and outer conductive members in the area of said helical convolutions, and means for applying an external DC magnetic field passing through said gyromagnetic material.

2. Structure in accordance with claim 1, including a rotatable rod means supporting said sphere for tuning said filter.

3. A coaxial microwave band preselector comprising: first and second lengths of coaxial tubing interconnected in relatively substantially parallel relation, each of said lengths of tubing including a hollow outer conductor member, an inner conductor member concentrically disposed with respect to said outer conductor member, said inner conductor members each includig a pair of coaxially arranged conductive segments, and a non-conductive segments having an outer surface, and interconnecting an end of each of said pair of conductive segments, a conductive wire disposed in helical convolutions upon said outer surface of said non-conductive segment, and connected to said conductive segments, a sphere of gyromagnetic material supported in the interstice between the inner conductors of said first and second lengths of coaxial tubing in the area of said helical convolutions, and means providing a DC magnetic field passing through said gyromagnetic material.

4. Structure in accordance with claim 3, including a rotatable rod means supporting said. sphere for tuning said filter.

References Cited UNITED STATES PATENTS 2,925,565 2/1960 Cook et a1. 3,013,229 12/1961 De Grasse. 3,022,470 2/1962 Oliner 333-241 3,368,169 2/1968 Carter et al. 33324.1

ELI LIEBERMAN, Primary Examiner PAUL L. GENSLER, Assistant Examiner U.S. c1. X.R. 333-73 

